One step closer to complex ‘Quantum Teleportation’ – University of Vienna


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Novel complex quantum entanglement generated in the laboratory for the first time

For future technologies such as quantum computers and quantum encryption, the experimental mastery of complex quantum systems is inevitable. Scientists from the University of Vienna and the Austrian Academy of Sciences have succeeded in making another leap.

While physicists around the world are trying to increase the number of two-dimensional systems, so-called qubits, researchers around Anton Zeilinger are breaking new ground. They pursue the idea to use more complex quantum systems as qubits and thus can increase the information capacity with the same number of particles.

The developed methods and technologies could in the future enable the teleportation of complex quantum systems. The results of their work “Experimental Greenberger-Horne-Zeilinger Entanglement Beyond QuBits” is published recently in the renowned journal Nature Photonics.

Similar to bits in conventional computers, QuBits are the smallest unit of information in quantum systems. Big companies like Google and IBM are competing with research institutes around the world to produce an increasing number of entangled QuBits. The clear motivation is to develop a functioning quantum computer. A research group at the University of Vienna and the Austrian Academy of Sciences, however, is pursuing a new path to increase the information capacity of complex quantum systems.

quantum-satellite-record-1Quantum Teleportation Explained in the Nutshell

The idea behind it is simple: instead of just increasing the number of particles involved, the complexity of each system is increased. “The special thing about our experiment is that for the first time it entangles three photons beyond the conventional two-dimensional nature,” explains Manuel Erhard, first author of the study. For this purpose, the Viennese physicists use quantum systems which have more than two possible states – in this particular case, the angular momentum of individual light particles. These individual photons now have a higher information capacity than QuBits.

However, the entanglement of these light particles turned out to be difficult on a conceptual level. The researchers overcame this challenge with a ground-breaking idea: a computer algorithm that autonomously searches for an experimental implementation.

Also Read About: Chinese satellite shatters quantum teleportation distance record

With the help of the computer algorithm Melvin an experimental setup to produce this type of entanglement has been uncovered. At first this was still very complex, but at least it worked in principle. After some simplifications, physicists still faced major technological challenges. The team was able to solve these with state-of-the-art laser technology and a specially developed multi-port. “This multi-port is the heart of our experiment and combines the three photons so that they are entangled in three dimensions,” explains Manuel Erhard.

The peculiar property of the three-photon entanglement in three dimensions allows for experimental investigation of new fundamental questions about the behaviour of quantum systems. In addition, the results of this work could also have a significant impact on future technologies, such as quantum teleportation. “I think the methods and technologies that we developed in this publication allow us to teleport a higher proportion of the total quantum information of a single photon, which could be important for quantum communication networks,” Anton Zeilinger points out into the future of possible applications.

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Publication in Nature Photonics: „Experimental Greenberger-Horne-Zeilinger Entanglement Beyond QuBits”, Manuel Erhard, Mehul Malik, Mario Krenn & Anton Zeilinger. https://doi.org/10.1038/s41566-018-0257-6

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‘Quantum Internet’ – Moving toward ‘Unhackable’ Communications and how Single Particles of Light could make it Possible: Purdue University – Next Step ‘On-Chip Circuitry’


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Purdue researchers have created a new light source that generates at least 35 million photons per second, increasing the speed of quantum communication. Credit: Massachusetts Institute of Technology image/Mikhail Shalaginov

Hacker attacks on everything from social media accounts to government files could be largely prevented by the advent of quantum communication, which would use particles of light called “photons” to secure information rather than a crackable code.

The problem is that quantum communication is currently limited by how much   can help send securely, called a “secret bit rate.” Purdue University researchers created a new technique that would increase the secret bit rate 100-fold, to over 35 million photons per second.

“Increasing the bit rate allows us to use single photons for sending not just a sentence a second, but rather a relatively large piece of information with extreme security, like a megabyte-sized file,” said Simeon Bogdanov, a Purdue postdoctoral researcher in electrical and computer engineering.

Eventually, a high  will enable an ultra-secure “quantum internet,” a network of channels called “waveguides” that will transmit single photons between devices, chips, places or parties capable of processing quantum information.

“No matter how computationally advanced a hacker is, it would be basically impossible by the laws of physics to interfere with these quantum communication channels without being detected, since at the quantum level,  and matter are so sensitive to disturbances,” Bogdanov said.

The work was first published online in July for inclusion in a print Nano Letters issue on August 8, 2018.

Using light to send information is a game of probability: Transmitting one bit of information can take multiple attempts. The more photons a light source can generate per second, the faster the rate of successful information transmission.

Toward unhackable communication: Single particles of light could bring the 'quantum internet'
The Purdue University Quantum Center, including Simeon Bogdanov (left) and Sajid Choudhury (right), is investigating how to advance quantum communication for practical uses. Credit: Purdue University image/Susan Fleck

“A source might generate a lot of photons per second, but only a few of them may actually be used to transmit information, which strongly limits the speed of quantum communication,” Bogdanov said.

For faster  , Purdue researchers modified the way in which a light pulse from a laser beam excites electrons in a man-made “defect,” or local disturbance in a crystal lattice, and then how this defect emits one  at a time.

The researchers sped up these processes by creating a new light source that includes a tiny diamond only 10 nanometers big, sandwiched between a silver cube and silver film. Within the nanodiamond, they identified a single defect, resulting from one atom of carbon being replaced by nitrogen and a vacancy left by a missing adjacent carbon atom.

The nitrogen and the missing atom together formed a so-called “nitrogen-vacancy center” in a diamond with electrons orbiting around it.

A metallic antenna coupled to this defect facilitated the interaction of photons with the orbiting electrons of the nitrogen-vacancy center, through hybrid light-matter particles called “plasmons.” By the center absorbing and emitting one plasmon at a time, and the nanoantenna converting the plasmons into photons, the rate of generating photons for  became dramatically faster.

“We have demonstrated the brightest single-photon source at room temperature. Usually sources with comparable brightness only operate at very low temperatures, which is impractical for implementing on computer chips that we would use at room temperature,” said Vlad Shalaev, the Bob and Anne Burnett Distinguished Professor of Electrical and Computer Engineering.

Next, the researchers will be adapting this system for on-chip circuitry. This would mean connecting the plasmonic antenna with waveguides so that photons could be routed to different parts of the chip rather than radiating in all directions.

 Explore further: Physicists demonstrate new method to make single photons

More information: Simeon I. Bogdanov et al. Ultrabright Room-Temperature Sub-Nanosecond Emission from Single Nitrogen-Vacancy Centers Coupled to Nanopatch Antennas, Nano Letters (2018). DOI: 10.1021/acs.nanolett.8b01415